This invention relates to liquid detergent compositions and more particularly to liquid laundry detergent compositions containing polymeric acetal carboxylate builders, and component solutions useful in the formulation thereof.
Materials known as "builders" are characterized by their capability for improving detergency levels of soaps and synthetic detergent compositions.
Builders exhibit a variety of performance properties which permit the attainment of better cleaning performance than is possible when so-called unbuilt compositions are used. The behavior mechanisms by which builders perform their function are only partially understood. It is known that good builders must be able to sequester most of the calcium and/or magnesium ions in the wash water since these ions are detrimental to the detergency process. However, it is difficult to predict which class of compounds possess useful combinations of builder properties and which compounds do not, because of the complex nature of detergency and the countless factors which contribute both to overall performance results and the requirements of environmental acceptability.
Conventionally, sodium tripolyphosphate (STP) has been a preferred and widely used detergent builder. However, because of the recent emphasis on removing phosphates from detergent and cleaning compositions for environmental reasons, the detergent and cleaning industry is now looking for materials suitable for use as builders which do not contain phosphorus and which are environmentally accepted.
Crutchfield et al U.S. Pat. No. 4,144,226 describes polymeric acetal carboxylates which are comprised of a series of repeating units corresponding to the formula ##STR1## in which M is selected from among alkali metal, ammonium, alkyl groups having from 1-4 carbon atoms, tetraalkyl ammonium groups, and alkylamine groups having from 1 to about 4 carbon atoms in the alkyl chain; and n averages at least 4. To provide chemical stability, the polymer chain is provided with stabilizing end cap group so that the complete molecule corresponds to the formula ##STR2## in which R.sup.1 and R.sup.2 are individually any chemically stable group which stabilizes the polymer against rapid depolymerization in the alkaline environment typical of wash solutions containing detergent. Particular groups which may comprise R.sup.1 and R.sup.2 include moieties derived from otherwise stable compounds such as alkanes, alkenes, branched chain hydrocarbons, both saturated and unsaturated, aromatic hydrocarbons, haloaklanes, alcohols, mercaptans, ethers, aldehydes, ketones, carboxylic acids, carboxylic acid salts, carboxylic acid esters, and carboxylic anhydrides.
As described, for example, in Crutchfield et al U.S. Pat. No. 4,140,676, the polymeric acetal carboxylates are prepared by polymerization of an ester of glyoxylic acid. For use as a builder, the resultant poly(glyoxylic acid ester) is preferably saponified to produce a salt. As described in Crutchfield et al U.S. Pat. No. 4,144,226 and a number of other patents, saponification is preferably carried out with sodium hydroxide to produce the sodium salt. Generally, the sodium salt represents the preferred species for use in formulating powder form detergents.
Polymeric acetal carboxylate builders are attractive because they are resonably resistant to degradation in alkaline solution and, thus, sufficiently stable to perform their function in the alkaline environment of washing or cleaning operations. However, these compositions are readily degradable in acidic solutions, and thus do not persist in the environment but instead are easily consumed in the course of conventional sewage treatment.
While detergents can be formulated in either solid or liquid form, solid powder has long been the commercially predominant form. Production, shipment and storage of the detergent in this form allows considerable latitude with regard to the solubility and hydrolytic stability of the builder. Recently, however, there has been a strong trend in the laundry detergent market for conversion from solid powder to liquid form products. Liquid detergents offer convenience to the user, but the formulation, shipment and storage of liquid detergents require a builder having substantial solubility and hydrolytic stability.
While the sodium salts of polymeric acetal carboxylates have more than sufficient solubility to function effectively in wash water, where the concentration of detergent may be in the range of 0.1 to 0.5% by weight, the sodium salts do not have the degree of solubility desirable for concentrated liquid detergent formulations. A high level of solubility is desired to permit the preparation of a concentrated liquid product, and also to minimize the amount of water brought into the formulation from the ingredient solution through which the builder is incorporated. In the formulating of liquid detergents, the various components are typically dissolved separately in water to produce a plurality of component solutions, and then these solutions are blended to produce the final product. The higher the feasible concentration of one component solution, the greater is the latitude provided with regard to other components; and the process of formulating thereby facilitated.
Although the sodium salt of an acetal carboxylate polymer has more than sufficient hydrolytic stability to serve its function in the washing-process, the sodium salt is subject to degradation over time when contained in aqueous solution, even one of optimal alkaline pH. A need has, therefore, existed for formulations which contain a form of polymeric acetal carboxylate salt which is both highly soluble and hydrolytically stable in aqueous liquid detergent compositions and the alkaline component solutions from which they are formulated.
Most of the prior work with polymeric acetal carboxylate builders has been directed toward powder form detergent formulations in which, as noted, the sodium salt is preferred. However, Crutchfield et al U.S. Pat. No. 4,144,226 makes passing reference to liquid dishwashing formulations, noting that they normally contain about 20 percent to about 45 percent surfactant, and that the weight ratio of surfactant to builder typically is in the range of 1:12 to 2:1. In another place, Crutchfield et al state that in some formulations, whether greater builder solubility is required, the use of ammonium or alkanolammonium salts may be desirable.
DelGreco et al U.S. Pat. No. 4,438,024 and Hughes U.S. Pat. No. 4,507,219 both contain disclosure of liquid detergent compositions which contain or may contain polyacetal carboxylate type builders. Hughes, in particular, discloses a relatively complex composition which is specified as containing a mix of potassium and sodium ions, in a potassium to sodium molar ratio of between about 0.1 and about 1.3. However, Hughes does not associate the K.sup.+ or Na.sup.+ ions with the builder; and neither Hughes nor DelGreco contains any teaching regarding the particularly form of polyacetal carboxylate salt to be used in the formulation. Moreover, each of these references discloses a plethora of different polycarboxylate builders, neither reference expresses any preference for polyacetal carboxylates, and neither contains any actual examples of formulations containing polyacetal carboxylates.
Aqueous liquid detergent compositions can be formulated in both homogeneous solution and emulsion form. In the case of a homogeneous solution, the surfactant and builder are present in colloidal micelles dispersed in the solvent, and may also be present to an extent in true solution. Generally, the homogeneous solution form is preferred because of its clarity and stability. However, relatively high concentrations of surfactant and builder can more readily be provided by resort to emulsion formulations. Especially high concentrations can be realized by preparation of the composition in the form of a gel or paste. For certain applications, these latter forms may be satisfactory. However, for most consumer laundry detergent applications, the homogeneous solution form is strongly preferred.
By use of cosolvents such as lower molecular weight alcohols or glycols, the solubility of sparingly soluble builders and other components can be increased. However, the use of alcohols or glycols adds to the expense of the detergent composition and may create additional problems or complications in the process of its formulation. Thus, there has been a particular need for forms of acetal carboxylate polymer salts which can be incorporated in substantial proportions in homogeneous aqueous solution, preferably without the need for cosolvents such as alcohols or glycols.